The formation of the body pattern during embryogenesis of the chironomid midge Smittia is under control of morphogenetic determinants localized near the anterior pole of the egg. These determinants apparently represent cytoplasmic ribonucleoprotein particles; their inactivation causes the formation of "double abdomens" with an additional abdomen in place of head and thorax. Proposed experiments: (1) The localization of anterior determinants will be analyzed by the kinetics of double abdomen yields after UV irradiation with different egg orientations at successive stages of development. These changes will be correlated with changes in the egg architecture and in the localization of radioactive poly(U)-probes hybridized in situ to egg sections. (2) Eggs programmed to develop into double abdomens will be used to test the ability of transplanted fractions to reprogram ("rescue") eggs to form the normal segment pattern. This bioassay should reveal the molecular nature of the anterior determinants and their origin during oogenesis. (3) Indicator proteins signaling the abnormal development before it becomes morphologically apparent will be analyzed by two-dimensional gel electrophoresis. We will compare the proteins synthesized in anterior versus posterior egg halves, in normal and UV irradiated eggs, with only maternal or both maternal and embryonic messenger RNA as templates.